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4. Nasal cavity
The nasal cavity forms part of the aerodigestive tract. The nasal cavity is formed by : * anteriorly: nasal aperture * laterally: (anterior to posterior) the maxilla (nasal and frontal process) with the inferior, middle and superior nasal conchae or turbinates, perpendicular plate of the palatine bone and medial pterygoid plate. * superiorly: sphenoid, cribiform plate of the ethmoid bone, nasal spine of the frontal bone and nasal bone. * inferiorly: palatal processes of the maxilla and horizontal portion of the palatine bone. Anteriorly the small opening leads to an incisive canal traversed by the nasopalatine nerve and greater palatine artery. Nasal septum: In the midline, the nasal cavity is divided into right and left halves by a septum composed of: *fibrocartilage *vomer posteriorly (articulating to the sphenoid posterior) *perpindicular plate of the ethmoid bone anteriorly. Anteriorly, it is continuous with the nose at the nasal aperture and posteriorly it is continuous with the nasopharynx. Laterally, the three nasal conchae form three spaces inferiorly: Turbinates *Bony superior, middle, and inferior turbinates project medially into nasal cavity *Define region below as superior, middle, and inferior meatuses, respectively *Middle turbinate attaches superiorly to cribriform plate via vertical lamella and posteriorly and laterally to lamina papyracea via basal lamella Meatus * superior meatus: ** posterior ethmoidal air cells and sphenoid sinuses via the spheno-ethmoidal recess * middle meatus: the ethmoid bulla underlies this, which is a convex bulge formed by the middle ethmoidal air cells. The slit in front of the bulla and behind the uncinate process is the semi-lunaris hiatus. This leads into the ethmoidal infundibulum, a curved cleft bordered medially by the uncinate process and laterally by the orbital plate of the ethmoid. These structures are collectively the osteomeatal complex that drains ** frontal sinus via frontal recess ** ethmoid and maxillary sinuses * inferior meatus: ** nasolacrimal duct The sphenopalatine foramen opens at the posterior end of the middle concha. The attachment of the middle concha, divide the ethmoidal cells into anterior and posterior systems. Blood supply Arterial supply The arterial supply of the nasal cavity is rich and derives from both the internal and external carotid arteries. The main artery is the sphenopalatine. * lateral nasal wall ** superior lateral nasal wall: anterior and posterior ethmoidal arteries ** inferior and middle turbinates: sphenopalatine artery ** posterior lateral nasal wall: pharyngeal artery * septum ** anteriorly: greater palatine artery (through the incisive canal) ** postero-inferiorly: sphenopalatine artery ** superiorly: anterior and posterior ethmoid branches ** septal branch of superior labial * floor ** greater palatine and superior labral arteries Rich arterial supply results in two anastomotic areas, which are common sites of epistaxis: * Woodruff area: anastomosis of sphenopalatine and pharyngeal arteries in the inferior lateral nasal wall, posterior to the inferior turbinate * Kiesselbach plexus: anastomosis of the anterior ethmoid, greater palatine, sphenopalatine and superior labial arteries in the anteroinferior nasal septum Venous drainage A rich venous submucosal venous network is formed by veins that accompany arteries. These include pterygoid plexus, facial vein and ophthalmic vein. Rarely 1% an emissary vein transverse the foramen caecum and connect nasal veins to the superior sagittal sinus. It should be noted that the posterior ethmoid veins anastomose with veins of the dura mater and orbit, making this a potential route of spread of infection. There is also an anastomosis with veins of the external nose. Lymphatic drainage * anterior drainage: to the external nose 6 * posterior drainage: via separate pathways to the lateral pharyngeal lymph nodes or deep cervical chain 6